It is an industry standard that is treated as a necessity to make light sources as small as possible. This saves material costs, and can improve optical imaging. In competition with these needs, large fields areas may need to be illuminated, and with vehicle illumination, a substantial visual image is needed on the surface of the vehicle to mark the presence of the vehicle. These goals have been met in the past by the use of relatively large incandescent lamp and reflector systems. The advent of solid-state lighting has pointed in the direction of improving these systems by drastically reducing the size of the light source; however, there is still a need to spread beam-forming illumination over a broad area to better illuminate the vehicle. One successful approach to solving this problem is disclosed in the above-identified application and is shown in FIGS. 1 and 2 herein. Referring now to FIGS. 1 and 2, there is shown an optical light guide 10a that can be utilized with a replaceable lamp assembly 10. The light guide 10a comprises a substantially trumpet-shaped, rigid light transmissive body 12a having an input widow 14, a distal end 16, a front side 18, and a rear side 20. The light transmissive body 12a has a substantially smooth exterior surface on the front side 18 and a substantially clear and solid interior. A preferred material for the light guide body is a clear plastic.
The input window 14 transmits light received from the LEDs into the light transmissive body 12a and extends substantially transverse to a longitudinal axis 12c of the replaceable lamp assembly 10.
The light transmissive body 12a has a substantially constant thickness measured between the front side 18 and the rear side 20 and extends away from the input window 14 through an arc of from 60 to 120 degrees, with 90° being preferred, to an extension 21 that forms an output region 22 that extends towards the distal end 16.
The rear side 20 at least in the output region 22 is formed with a plurality of reflective steps 24 using total internal reflection to direct a portion of the intercepted light towards the front side 18.
The front side 18 of the output region 22 can be formed with refractive features directing light received from the reflective steps 24 in a desired direction.
The extension 21 of the output region 22 comprises about one third of the surface distance from the input window 14 to the distal end 16 while the entire length from the input window 14 to the distal end 16 is more than 10 times the average thickness.
A difficulty with the trumpet-shaped optic described above arises when the area beneath the optic, which typically is an automotive fender, comprises a more or less compound curve. It would, therefore, be an advance in the art if a suitable optic could be developed that is simple to construct and capable of matching or accommodating a complex curvature.